1. Field of the Invention
The present invention is in the field of gas analysis and specifically relates to a sample chamber for use with a source of coherent radiation, such as a semiconductor laser, and capable of measuring the concentrations of several gases simultaneously.
2. The Prior Art
Numerous gas sample chambers are known in the art. Normally the design of a gas sample chamber is based on the task which the gas analyzer is expected to perform. The designer has a wide range of components at his disposal, and his design generally consists of a carefully selected combination of components. Each of the following references shows one or more components that are used in the present invention. However, none of the references shows the unique combination that is used in the present invention.
In U.S. Pat. No. 5,060,508 issued Oct. 29, 1991, Wong describes a gas sample chamber consisting of a hollow serpentine passage that extends within a block of a plastic material. An ellipsoidal reflector focuses radiation from a source into the passage, and a detector is located at the other end of the passage.
In U.S. Pat. No. 5,053,754 issued Oct. 1, 1991, Wong describes a fire detector in which a source of radiation, which may be a laser diode, injects radiation having a wavelength corresponding to an absorption band of the gas (CO.sub.2) into a hollow passage that guides the radiation along an indirect path to a detector. A semipermeable membrane is used to keep unwanted particles out of the passage.
In Japanese Laid-Open Patent Application No. 59-173734, filed on Mar. 23, 1983 and laid open on Oct. 1, 1984, Miyazaki shows a gas analyzer that has a single source of infrared radiation, a single detector and hollow tubes through which the radiation passes from the source to the detector.
In U.S. Pat. No. 4,709,150, Burough et al. show a gas analyzer in which a source of infrared radiation, which they state could be a semiconductor laser, is located at one end of a porous tube and in which a detector is located at the other end of the porous tube. Burough et al. do not disclose the use of specular reflections from the inside surface of their porous tube. The gas to be detected diffuses through the walls of the porous tube.
In U.S. Pat. No. 5,163,332 issued Nov. 17, 1992, Wong describes a diffusion-type gas sample chamber that employs an elongated hollow tube having a specularly-reflective inner surface and a plurality of filtering apertures each covered by a semipermeable membrane to keep out unwanted particles while permitting free diffusion of gas into and out of the sample chamber.